1. Technical Field
The present disclosure generally relates to techniques for preparing electronic devices, such as integrated circuit dies, chips, packages, boards, and the like, for failure analysis. More particularly, and not by way of any limitation, the present disclosure is directed to an apparatus and method for detecting an endpoint during removal of material from the sample.
2. Description of Related Art
During failure analysis of integrated circuits (ICs), whether in chips, packages, boards, etc., it is often necessary to create access to specific portions of the IC. Methods of creating these access points include at least chemical, laser, mechanical and plasma usage, yet each method of creating access brings its own problems. Laser decapsulation is slow and places the surface at risk due to ablation damage through the glass beads. Additionally, non-uniformity of removal is problematic with both chemical and laser mechanisms. Physical removal methods, such as milling, grinding and polishing, provide greater planarity of removal, but the process, which is generally performed with a liquid or paste surrounding the moving tip, obscures visibility of the surface of the device-under-test (DUT). In the past, mechanical methods have required iterative guesswork to reach the desired target. One would estimate the depth necessary to provide access without destroying features and perform mechanical removal, e.g., with a milling machine, to the desired depth. The device would then be removed from the milling machine, cleaned and dried, and taken to another machine, e.g., a microscope or electron microscope, for examination to determine whether the desired endpoint had been reached. If further removal of material was necessary, the process would be repeated as many times as necessary until the desired endpoint was reached.